This invention relates to a heating device and particularly to a gas combustor for heating the evaporator portion of a heat pipe.
In the development, testing and evaluation of heat engines such as Stirling cycle engines, an external heat input system frequently is necessary. Such heat input may be provided by using a heat pipe in which a working fluid undergoes vaporization in the evaporator portion of the heat pipe, and is transported to the condensor portion of the heat pipe or a Stirling engine where it condenses, giving up its latent heat of evaporation. The condensed working fluid is thereafter returned to the evaporator portion where the cycle is repeated in a continuous manner. A convenient form of heat energy for such applications is combusted hydrocarbon gases, such as liquified pertroleum gas or propane, etc. Accordingly, there is a need to provide a gas combustor apparatus which efficiently heats the evaporator portion of a heat pupe for providing a heated working fluid to an auxiliary utilization device such as a Stirling cycle engine.
In accordance with this invention, a combination gas combustor and heat pipe evaporator device is provided which features excellent thermal efficiency and is further relatively compact for a given heat transfer capacity. Efficiency of the device is achieved in part by providing a thin annular flue gas escape channel which provides a laminar flow regime for the flue gas which enhances heat transfer efficiency to a heat pipe evaporator. For both of the embodiments described herein, enhanced efficiency is further provided by a counter-flow inlet air heat exchanger which provides preheated combustion air which has the effect of boosting flue gas temperature, hereby increasing thermal efficiency.
In a first embodiment of this invention, an annular flue gas discharge channel is provided having a progressively decreasing radial width, which has the effect of decreasing flow Reynolds numbers with decreasing flue gas temperature as a means of causing heat transfer to the heat pipe evaporator to be more uniform along its length. In a second embodiment of this invention, a combination gas combustor and heat pipe evaporator is provided in which both the inner and outer radial walls of the annular flue gas discharge channel form portions of the heat pipe evaporator, which has the effect of reducing the overall length of the combustor device for a given heat transport capacity. Both devices achieve compactness through a construction in which a number of interfitting tubes provide the various fluid flow paths. In addition, means are provided in each embodiment for efficiently distributing liquid heat pipe working fluid along the length of the evaporator to prevent "drying out" of localized areas of the evaporator.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.